var p = prompt("请输入圆的半径");
var pi = Math.PI;

//半径
console.log(p);
//周长
console.log(2 * pi * p);
//面积
console.log(p*p*pi);
document.querySelector("#a").value = p;
document.querySelector("#b").value = 2*pi*p;
document.querySelector("#c").value = p*p*pi;